replaced loader with spin({ url: 'panel.html' });

this is a big change that allowed to remove a lot of code and tests
with a very small refactoring overhead.

* There is no more custom loader.
  spin() is now the only one loader available and it uses ajax.
  This allowed to remove spin.loader and spin.xhrLoader (and related tests and files)

* Added onclick.js tests
  These tests describe what should happen when spin captures a click

* Tests helpers
  Changed call to spin.loader to use spin({ url: ... });
  Change toBecome* matchers to be less strict about its css classes.

* Added tests to describe the loading process

* Added tests to describe the loading panel

* Updated test runner

* Removed two files that were not used for a long time